I use the modified 9005 bulbs as my low beam lamps and PIAA Ion-Crystal bulbs for my foglights. I delfinately see a difference in snow and fog over the standard "white" bulbs.

The reason that yellow lamps are so commonly used as fog lights is because white/blue light is much more reflective than yellow. In snow or fog, you want your fog lamps to illuminate the ground just ahead of the vehicle, not the fog or snow.

Driving w/ my fog lights on I do have increased visibility of the road but I still focus out past the fog lights as they project much closer to the front of the car. It is a good idea to use the foglights only when needed to avoid focusing too close to the front of the car.

Tip: when shopping for bulbs I use Froogle and search for the bulb type number (9005, PIAA H3, etc..) and browse untill I find the best price. Don't forget to factor shipping. Cartoys wanted $84.99 for my Ion-Crystals... I had them shipped for less than $45! From a store called Racerwheel out of CA.